1. Field of the Invention
The invention relates to antioxidants and to lubricant compositions containing them. The antioxidants more particularly are hemi-hindered phenols containing a thiaalkene group in the ring.
2. Discussion of the Prior Art
It is well known that many organic liquids and solids used in industrial applications, such as oils and greases, power transmission fluids, resin and polymer coatings, insulations, structural products and the like, may deteriorate and lose their ability to function when subjected to oxidation. Since these substances are very often utilized at high temperatures, the rate of oxidation breakdown can be very rapid. This problem is particularly important in the operation of modern day automotive and aircraft engines. The breakdown of the lubricating oil, either natural or synthetic, is frequently accompanied by the formation of corrosive acids, sludge and other products of such breakdown. These resulting products can harm the metal surfaces of the engine and interfere with the efficient operation of the lubricants.
Phenols and alkylated phenols, particularly the hindered phenols, are well known agents for imparting oxidation protection to a wide variety of materials. For application to lubricants, fats and oils, and oil-containing food stuffs certain types of alkylated phenols known in the art as "hindered phenols" have been found to be particularly effective. For example 2,6-di-tert-butylphenol and 2,6-di-tert-4-methylphenol (known as BHT in foods and DBPC in lubricants) are widely utilized in such applications.